Luis G. Cabral-Rosetti

Rare top quark and Higgs boson decays in alternative left-right symmetric models

Top quark and Higgs boson decays induced by flavor-changing neutral currents (FCNC) are very much suppressed in the standard model. Their detection in colliders such as the Large Hadron Collider, Next Linear Collider, or Tevatron would be a signal of new physics. We evaluate the FCNC decays t{yields}H{sup 0}+c, t{yields}Z+c, and H{sup 0}{yields}t+c in the context of alternative left-right symmetric models with extra isosinglet heavy fermions; in this case, FCNC decays occur at tree level, and they are suppressed only by the mixing between ordinary top and charm quarks, which is poorly constrained by current experimental values. This provides the possibility for future colliders either to detect new physics or to improve present bounds on the parameters of the model.

Hydrodynamics of galactic dark matter

We consider simple hydrodynamical models of galactic dark matter in which the galactic halo is a self-gravitating and self-interacting gas that dominates the dynamics of the galaxy. Modelling this halo as a spherically symmetric and static perfect fluid satisfying the field equations of general relativity, visible baryonic matter can be treated as ‘test particles’ in the geometry of this field. We show that the assumption of an empirical ‘universal rotation curve’ that fits aw id ev ariety of galaxies is compatible, under suitable approximations, with state variables characteristic of a non-relativistic Maxwell–Boltzmann gas that becomes an isothermal sphere in the Newtonian limit. Consistency criteria lead to a minimal bound for particle masses in the range 30 eV <m< 60 eV and to a constraint between the central temperature and the particle mass. The allowed mass range includes popular supersymmetric particle candidates, such as the neutralino, axino and gravitino, as well as lighter particles (m ≈ keV) proposed by numerical n-body simulations associated with self-interactive CDM and WDM structure formation theories.

Appell Functions and the Scalar One-Loop Three-point Integrals in Feynman Diagrams

The scalar three-point function appearing in one-loop Feynman diagrams is compactly expressed in terms of a generalized hypergeometric function of two variables. Use is made of the connection between such Appell function and dilogarithms coming from a previous investigation. Special cases are obtained for particular values of internal masses and external momenta.

Empirical testing of Tsallis’ Thermodynamics as a model for dark matter halos

We study a dark matter halo model from two points of view: the “stellar polytrope” (SP) model coming from Tsallis’ thermodynamics, and the one coming from the Navarro‐Frenk‐White (NFW) paradigm. We make an appropriate comparison between both halo models and analyzing the relations between the global physical parameters of observed galactic disks, coming from a sample of actual galaxies, with the ones of the unobserved dark matter halos, we conclude that the SP model is favored over the NFW model in such a comparison.

Anapole moment of the lightest neutralino in the cMSSM

Abstract We study the anapole moment of the lightest neutralino in the constrained Minimal Supersymmetric Standard Model (cMSSM). The electromagnetic anapole is the only allowed electromagnetic form factor for Majorana fermions, such as the neutralino. Since the neutralino is the LSP in many versions of the MSSM and therefore a candidate for dark matter, its characterization through its electromagnetic properties is important both for particle physics and for cosmology. We perform a scan in the parameter space of the cMSSM and find that the anapole moment is different from zero albeit very small ( 10 − 3 GeV − 2 ). Combined with experimental constraints like the Higgs mass and the DM relic density, the allowed region of parameter space lies within the reach of future direct DM searches. Thus, the anapole moment could be used as a complementary constraint when studying the parameter space of the cMSSM and other similar models.

Dirac Neutrino Anapole Moment

We calculate the Dirac neutrino anapole moment (avl) in the context of the Standard Model (SM) making use of the Dirac form factor FD(q2) introduced recently by J. Bernabeu, L. G. Cabral‐Rosetti, J. Papavassiliou y J. Vidal by using the Pinch Technique (PT) formalism, working in two different gauge‐fixing schemes (Rξ guage and the electroweak BFM), at the one loop level. We show that the neutrino anapole form factor FA(q2) and Dirac form factor FD(q2) are related as follows: FA(q2) = 1q2FD(q2). Hence, the Dirac neutrino charge radius 〈rvl2〉 and the anapole moment satisfy the simple relation avl = 16〈rvl2〉. Therefore, we show that the anapole moment (as the charge radius) of the neutrino is a physical quantity, which only gets contribution from the proper neutrino electromagnetic vertex (in electroweak BFM), and that avl is of the order 10−34 cm2.We calculate the Dirac neutrino anapole moment (avl) in the context of the Standard Model (SM) making use of the Dirac form factor FD(q2) introduced recently by J. Bernabeu, L. G. Cabral‐Rosetti, J. Papavassiliou y J. Vidal by using the Pinch Technique (PT) formalism, working in two different gauge‐fixing schemes (Rξ guage and the electroweak BFM), at the one loop level. We show that the neutrino anapole form factor FA(q2) and Dirac form factor FD(q2) are related as follows: FA(q2) = 1q2FD(q2). Hence, the Dirac neutrino charge radius 〈rvl2〉 and the anapole moment satisfy the simple relation avl = 16〈rvl2〉. Therefore, we show that the anapole moment (as the charge radius) of the neutrino is a physical quantity, which only gets contribution from the proper neutrino electromagnetic vertex (in electroweak BFM), and that avl is of the order 10−34 cm2.

Constraining the mSUGRA parameter space through entropy and abundance criteria

We explore the use of two criteria to constrain the allowed parameter space in mSUGRA models; both criteria are based in the calculation of the present density of neutralinos χ0 as Dark Matter in the Universe. The first one is the usual “abundance” criterion that requieres that present neutralino relic density complies with 0.0945 < ΩCDMh2 < 0.1287, which are the 2σ bounds according to WMAP. To calculate the relic density we use the public numerical code micrOMEGAS. The second criterion is the original idea presented in [3] that basically applies the microcanonical definition of entropy to a weakly interacting and self‐gravitating gas, and then evaluate the change in entropy per particle of this gas between the freeze‐out era and present day virialized structures. An “entropy consistency” criterion emerges by comparing theoretical and empirical estimates of this entropy. One of the objetives of the work is to analyze the joint application of both criteria, already done in [3], to see if their results, usi...